Refinery sludges are typically mixtures of hydrocarbon oils, heavy residual hydrocarbons including asphaltenes, water and particulate solids. These sludges are produced from a number of refinery units, including various standard waste water treatment separators. These sludges often contain substances such as benzene, toluene, xylene, chrysene and the like which are "listed" by the Environmental Protection Agency (EPA) as hazardous substances.
Historically, refinery sludges have been economically disposed of by land-filling and land-farming techniques. However, land disposal is now regulated by the Resource Conservation and Recovery Act (RCRA) and the Hazardous and Solid Waste Amendments of 1984 (RITA), and has consequently become more difficult and expensive.
U.S. Pat. No. 4,341,619 discloses a process for recovering carbonaceous materials from tar sands by supercritical extraction involving countercurrent flow of the tar sand and a solvent. The solvents that are disclosed as being useful include aromatic hydrocarbons, alicyclic hydrocarbons having 5-16 carbon atoms, phenols, and nitrogen-containing compounds. This patent is incorporated herein by reference.
U.S. Pat. No. 4,434,028 discloses a method and apparatus for removing oil and other organic constituents from particulate, inorganic-rich mineral solids. The reference indicates that the disclosed method and apparatus are particularly suitable for removing oil from oil-contaminated drill cuttings. This patent is incorporated herein by reference.
The final report for EPA Contract No. 68-02-3924 which is entitled "Pilot Plant Evaluation of Critical Fluid Extractions for Environmental Applications" discloses the results of using liquified-gas solvents in a pilot plant to extract oil from steel mill scale and bleaching clay. This report is incorporated herein by reference.
There is a need for an efficient, economical and reliable process for treating refinery sludges to render the product solids delistable or to facilitate additional handling and treatment of the solids, e.g., treatment by cementing to prevent metals leaching. It would be advantageous if this process were adaptable to treating other solid and hazardous wastes as well as other solids/hydrocarbon-containing materials such as catalyst fines-containing streams (e.g., decanter oil streams from fluid catalytic cracking units), oil-contaminated drill cuttings, steel mill scale, bleaching clay and the like.